A variety files made of stainless steel (S-S) or nickel-titanium (Ni-Ti) are used during endodontic treatment. The purpose of this study was to evaluate the corrosion susceptibility of S-S and Ni-Ti endodontic files. Three brands of files were used for this study: K-flex® S-S files (Maillefer, USA), Profile® Ni-Ti files (Maillefer, USA), K-3® Ni-Ti files (SybronEndo, USA). 120 files of each brands (21mm, ISO size #20) were divided into 12 groups according to 1) sterilization methods using Autoclave or Ethylene Oxide (E-O) gas, 2) Irrigation solutions using 5.25 % NaOCl or Saline, 3) the number of sterilization (1, 5, 10 times). After above procedures, each of the files was inspected by three examiners with a light microscope and camera at X25. Each file was judged and ranked according to the following criteria: 0; no corrosion, 1; mild corrosion, 2; moderate corrosion, and 3; severe corrosion. The files of high score were examined under the Scanning Electron Microscope.

Data were statistically analyzed with the Kruskal-Wallis test (p < 0.05). Most of the ten time-autoclaved files had showed mild to moderate corrosion. But, one or five time-autoclaved files did not show corrosive surface. NaOCl treatment and E-O gas sterilization did not influence on corrosion. There was a significant difference in corrosion susceptibility between sterilization methods and the number of autoclaving. However, there was no significant difference between brands and file materials.

The purpose of this study was to investigate the effects of estrogen deficiency on pulpodentinal complex of tooth in ovariectomized rats. Thirty female Sprague-Dawley rats, 10 weeks old, were used. Rats were grouped into two groups. One group (n = 15) was subjected to sham surgery (SHAM) and the other group (n = 15) was ovariectomized bilaterally (OVX). Animals were sacrificed 12 weeks later, and their mandibular molars and associated periodontal supporting tissues were dissected out, and fixed in 10% buffered formalin. For comparison of groups, immunostained for osteonectin. Histomorphometrical measurement of change of teeth was performed using an image analysis system and paired t-test was used and the level of significance for overall differences was set at p < 0.05.

In immunostaining of osteonectin, they were significantly different from each other. The predentin thickness in OVX rats was wider than in SHAM rats. And in SHAM rats, osteonectin was more specifically stained in predentin areas than in OVX rats. These results indicate that estrogen deficiency increased the unmineralized predentin areas and decreased osteonectin content in pulpal tissues in rats. If our result is applicable to human studies, odotoblast is affected by estrogen deficiency.

The purpose of this study was to evaluate the apical sealing ability of Super-EBA, MTA and Dyract-flow as retrofilling materials. Forty-eight extracted human teeth with straight and single root canal were used in this study. The root canals were prepared to a #40 apical canal size and obturated with gutter-percha. Apicoectomies were performed and root end cavities were prepared to a depth of 3mm using an ultrasonic device. The root end cavities were filled with Super-EBA, MTA or Dyract-flow. Leakage was measured using an electrochemical technique for 4 weeks.

According to this study, the results were as follows.

1. Increasing leakage with time was observed in all groups.

2. No significant difference was noted among the 3 groups with time (p = 0.216).

3. No significant difference was noted among the 3 groups when measured within the same time interval (p = 0.814).

The results of this study suggest that the sealing ability of Dyract-flow is equal to that of Super-EBA and MTA, and Dyract-flow may be an alternative to other materials for root-end filling.